With this in mind, horizontal winds (also known as “crosswinds”) in excess of 30-35 kts (about 34-40 mph) are generally prohibitive of take-off and landing. As far as how this happens, it depends on where you are in flight.

There is no single universal "unsafe" number of knots for flying, as the limits depend heavily on the aircraft type, the runway orientation, and the phase of flight. For a large commercial jet like an Airbus A320, the maximum demonstrated crosswind limit for landing is typically around 33 to 38 knots. If the wind is a steady "headwind," planes can technically fly in very high speeds (even over 100 knots in the jet stream), as the wind actually helps provide more lift. However, ground operations usually stop when sustained winds or gusts exceed 40 to 50 knots, as it becomes unsafe to operate cabin doors, luggage loaders, or fuel trucks. Pilots and air traffic control constantly monitor these "knots" to ensure that takeoffs and landings only occur within the specific safety envelope designed by the aircraft manufacturer.